This invention relates to a manufacturing method and device for producing fluorescent lamps and such lamps produced thereby.
Fluorescent lamps are widely used in a variety of applications including image scanners and copy machines. In many of these applications, it is desirable for the fluorescent lamps to light-up, or stabilize their light levels, quickly and consistently, even when they have not operated for extended periods of time. For example. many owners of image scanners do not use them frequently. However, these owners expect their scanners to consistently and quickly operate when needed with minimal warm-up time.
Despite the benefits offered by fluorescent lamps and the desirability for them to light quickly, their basic structure typically requires some warm-up time before they are able to produce the desired levels of light. In general, a typical fluorescent lamp generates light by energizing a pair of spaced-apart electrodes positioned within a phosphor-coated sealed tube of a vapor containing mercury. Electrons from one of the electrodes pass through the vapor to the other electrode, thereby exciting the mercury and causing it to emit ultra-violet light. The ultra-violet light then interacts with the phospher coating to produce visible light. A very large number of these interactions must take place before a usable level of visible light is generated.
Residual heat generated by these interactions facilitates new interactions and thereby helps sustain the continued operation of the lamp. However, a lamp that has not been used for an extended period must typically generate a sufficient level of heat before a sufficient number of electron/mercury and ultra-violet/phosphor interactions are achieved to produce meaningful visible light. This time is often called the warm-up time of the fluorescent bulb.
In general, there are two types of electrodes used in fluorescent bulbs: hot-cathode electrodes and cold-cathode electrodes. Hot-cathode electrodes include a resistive filament, which like a filament in an incandescent bulb, is heated by current passing through it. This heat facilitates operation of the lamp. However, these hot-cathode filaments are fragile and require particularly complex electrical circuitry to operate effectively in this scanning environment.
Cold-cathode electrodes do not rely on additional means for generating heat besides that created by the electrical discharge through the fluorescent tube. As a result, they are typically easier to miniaturize because of the simplified electrode and reduced complexity of their driving electronics. Moreover, because they lack a fragile filament, they are more durable and usually last longer than hot-cathode fluorescent bulbs. Accordingly, cold-cathode electrodes in fluorescent lamps, which are commonly known as cold-cathode fluorescent lamps (xe2x80x9cCCFLxe2x80x9d), are typically used in miniaturized applications such as in desktop scanners. However, because CCFL lamps rely exclusively on the heat generated by the electrical discharge through the fluorescent tube, they typically have longer warm-up times than similarly sized hot-cathode fluorescent lamps.
A variety of devices and processes have been developed in an attempt to improve the warm-up time of fluorescent lamps. For example, U.S. Pat. No. 5,907,742 to Johnson et al. teaches using a variety of the system""s electronics to provide high voltage overdrive during early lamp warm-up, closed loop light level control, and periodic lamp warming during standby, to quickly warm-up and maintain the lamp""s heat and thereby decrease its warm-up time during use. In addition, U.S. Pat. No. 5,029,311 to Brandkamp et al. physically wraps the fluorescent lamp in a heater blanket in an attempt to maintain the same constant lamp temperature profile during both the lamp operation cycle and during standby. While these devices improve lamp warm-up time, the increased electronics and/or hardware also increase the complexity and expense of the products incorporating them, as well as increasing power consumption.
There have also been attempts to improve the specific construction and methods for manufacturing fluorescent lamps themselves. For example, U.S. Pat. No. 6,174,213 to Paz de Araujo et al. teaches a specialized method for applying a thin-film layer of conductive metal oxide to the inner lamp wall surface. In particular, a solution of metal precursor compound is allowed to distribute itself around the inner surface of the lamp before a solid metal oxide layer is formed by heating the liquid metal precursor. These additional processes increase the cost of manufacturing these lamps.
Similarly, other ways for releasing mercury vapor within a sealed lamp during the manufacturing process have also been considered. For example. U.S. Pat. No. 5,520,560 to Schiabel et al. heats a solid compound containing mercury to a temperature in excess of 500xc2x0 C. to thereby vaporize the mercury in the solid compound and release it within the sealed chamber. Despite these improvements, fluorescent lamps, and in particular CCFL lamps, still tend to have long warm-up times. Moreover, similar lamps manufactured using the same techniques often have a large variability in their individual warm-up times.
The invention is a method for producing a fluorescent lamp, and the lamp thereby produced using the method, that includes assembling the fluorescent lamp having a sealed chamber containing mercury and then uniformly heating the chamber along its length to a temperature above the vaporization temperature of the mercury to vaporize the mercury and thereby evenly disburse the mercury within the chamber.